The invention relates generally to a color electronic reprographic printing system, and more particularly concerns an apparatus for controlling the movement of a sheet to which is applied a plurality of developed images transferred thereto and the movement of a sheet gripper to prevent the image-bearing surface of the sheet from touching stationary surfaces in the printing system while the sheet is moving in a recirculating path.
The marking engine of an electronic reprographic printing system is frequently an electrophotographic printing machine. In an electrophotographic printing machine, a photoconductive member is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive member is thereafter selectively exposed. Exposure of the charged photoconductive member dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive member, the latent image on the photoconductive member which is subsequently transferred to a copy sheet. The copy sheet is heated to permanently affix the toner image thereto in image configuration.
Multi-color electrophotographic printing is substantially identical to the foregoing process of black and white printing. However, rather than forming a single latent image on the photoconductive surface, successive latent images corresponding to different colors are recorded thereon. Each single color electrostatic latent image is developed with toner of a color complementary thereto. This process is repeated a plurality of cycles for differently colored images and their respective complementarily colored toner. Each single color toner image is transferred to the copy sheet in superimposed registration with the prior toner image. This creates a multi-layered toner image on the copy sheet. Thereafter, the multi-layered toner image is permanently affixed to the copy sheet creating a color copy. The developer material may be a liquid or a powder material.
In the process of black and white printing, the copy sheet is advanced from an input tray to a path internal the electrophotographic printing machine where a toner image is transferred thereto and then to an output catch tray for subsequent removal therefrom by the machine operator. In the process of multi-color printing, the copy sheet moves from an input tray through a recirculating path internal to the printing machine where a plurality of toner images is transferred thereto and then to an output catch tray for subsequent removal. With regard to multi-color printing, a sheet gripper secured to a transport receives the copy sheet and transports it in a recirculating path enabling the plurality of different color images to be transferred thereto. The sheet gripper grips one edge of the copy sheet and moves the sheet in a recirculating path so that accurate multi-pass color registration is achieved. In this way, magenta, cyan, yellow, and black toner images are transferred to the copy sheet in registration with one another.
Toner is applied to the photoconductive member by a developer unit that contains a relatively small quantity of toner material mixed with magnetic carrier particles. The supply of toner material in the developer unit is diminished during application of toner images to the photoconductive member and must be replenished. Typically, a toner reservoir is attached directly to the developer unit. This direct attachment minimizes cost and problems with conducting toner material from a remote reservoir. The reservoir itself is typically refilled or replaced by the user. In color electrophotographic systems, four toner reservoirs and four developer units are required. Since limited space available in the printing machine dictates that multiple toner reservoirs attached directly to developer units be small, requiring frequent refill or replacement of the toner reservoirs, remote reservoir placement is particularly desirable.
One particular problem with remote reservoir placement is providing for an interface between the toner reservoirs and the developer units. Developer units are typically mounted in a drawer that is slidable relative to the chassis of the electrophotographic system between an operative position and a service position for access by the user or service personnel. However, remote toner reservoirs are mounted in the chassis of the system in a location readily accessible by the user for replenishment. Thus, a connection is required between the movable developer units and the stationary toner reservoirs. To prevent both loss of toner and contamination of the system's interior with toner, this connection must reliably close off the outlets from the toner reservoirs when the developer units are moved away from the reservoirs and must provide for clean re-engagement with the developer unit. However, in complex moving assemblies such as the sliding drawer with the attached developer units, small dimensional variations in component parts can stack up to relatively large quantities across the interface between the stationary toner reservoir and the sliding developer unit. This makes a reliable and clean connection difficult to achieve.
In color electrophotographic systems, each of the multiple toner image is transferred by a corresponding developer unit. The developer unit transferring an image is in an active position in close proximity with the photoconductive member, while the remaining units are displaced away from the photoconductive member in non-active positions. The developer units are thus movable between active and non-active positions within the slidable drawer. The interface of a stationary toner reservoir with a corresponding developer unit is complicated by the movement of the developer units between the active and non-active positions. Further, it is desirable that the developer unit be supplied with toner material in both its active and non-active positions because this allows slower toner input, which enhances mixing of newly-added toner with the developer material already in the developer unit.
There is thus a need for an interface between a stationary toner reservoir and a developer unit movable in two senses--between active and non-active positions relative to the photoconductive member and between operative and service positions relative to the system chassis.